System and method for an electrical de-icing coating

ABSTRACT

A system for modifying ice adhesion strength of ice adhered to an object comprises a composite coating containing wire electrodes covering the surface to be protected. In one embodiment, a composite coating contains electrode wires and insulator fibers. The composite coating is applied to the surface of an object on which the ice adhesion strength is to be modified. The electrode wires are connected to a dc bias source, and they function as cathodes and anodes alternately. The source generates a DC bias to an interface between the ice and the surface when the ice completes the circuit between anode and cathode wires. In another embodiment, a wire mesh is disposed on an electrically conductive surface of the object an opposing DC biases are applied to the mesh and the surface. In another embodiment, the coating has anode and cathode wires woven by insulator fibers as a composite cloth applied to the surface to protect the surface from ice.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application which claims thepriority of prior application Ser. No. 09/426,685, filed Oct. 25, 1999,entitled “Method And Apparatus For Modifying Ice Adhesion Strength”, nowU.S. Pat. No. 6,027,075 which is hereby incorporated by reference intothis application which claims the benefit of Provisional Application No.60/173,920, filed Dec. 30, 1999.

U.S. GOVERNMENT RIGHTS

This invention was made in part with the support of the U.S. Government;the U.S. Government has certain rights in this invention as provided forby the terms of Grant #DAAH 04-95-1-0189 awarded by the Army ResearchOffice and of Grant #MSS-9302792 awarded by the National ScienceFoundation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to methods, systems and structures for modifyingice adhesion strength between ice and selected objects. Moreparticularly, the invention relates to methods, systems and structuresthat apply electrical energy to the interface between ice and objects soas to either increase or decrease the ice adhesion strength tofacilitate desired results.

2. Statement of the Problem

Ice adhesion to certain surfaces causes many problems. For example,excessive ice accumulation on aircraft wings endangers the plane and itspassengers. Ice on ship hulls creates navigational difficulties, theexpenditure of additional power to navigate through water and ice, andcertain unsafe conditions. The need to scrape ice that forms onautomobile windshields is regarded by most adults as a bothersome andrecurring chore; and any residual ice risks driver visibility andsafety.

Icing and ice adhesion also causes problems with helicopter blades, andwith public roads. Billions of dollars are spent on ice and snow removaland control. Ice also adheres to metals, plastics, glasses and ceramics,creating other day-to-day difficulties. Icing on power lines is alsoproblematic. Icing adds weight to the power lines which causes poweroutages, costing billions of dollars in direct and indirect costs.

In the prior art, methods for dealing with ice adhesion vary, thoughmost techniques involve some form of scraping, melting or breaking. Forexample, the aircraft industry utilizes a deicing solution such as ethylglycol to douse aircraft wings so as to melt the ice thereon. Thisprocess is both costly and environmentally hazardous; however, the riskto passenger safety warrants its use. Other aircraft utilize a rubbertube aligned along the front of the aircraft wing, whereby the tube isperiodically inflated to break any ice disposed thereon. Still otheraircraft redirect jet engine heat onto the wing so as to melt the ice.

These prior art methods have limitations and difficulties. First,prop-propelled aircraft do not have jet engines. Secondly, rubber tubingon the front of aircraft wings is not aerodynamically efficient. Third,de-icing costs are extremely high, at $2500-$3500 per application; andit can be applied up to about ten times per day on some aircraft. Withrespect to other types of objects, heating ice and snow is common. But,heating of some objects is technically impractical. Also, large energyexpenditures and complex heating apparati often make heating tooexpensive.

The above-referenced problems generally derive from the propensity ofice to form on and stick to surfaces. However, ice also createsdifficulties in that it has an extremely low coefficient of friction.Each year, for example, ice on the roadway causes numerous automobileaccidents, costing both human life and extensive property damage. Ifautomobile tires gripped ice more efficiently, there would likely befewer accidents.

U.S. Pat. No. 6,027,075, incorporated herein by reference, disclosescertain embodiments of an invention in which electrical energy in theform of a direct current (“DC”) bias is applied to the interface betweenice and the object that the ice covers. As a result, the ice adhesionstrength of the ice to the surface of the object is modified. Typically,the ice adhesion strength is decreased, making it possible to remove icefrom the object by wind pressure, buffeting or light manual brushing. Inother applications, the ice adhesion strength between ice and surfacesof objects in contact with the ice are increased. For example, when theice adhesion strength is increased between automobile tires and icyroadways, there is less slippage and fewer accidents. In general, if acharge is generated at the interface of ice in contact with a object, itis possible to selectively modify the adhesion between the ice and theobject.

In general, U.S. Pat. No. 6,027,075 discloses a power source connectedto apply a DC voltage across the interface between ice and the surfaceupon which the ice forms. By way of example, the object having theconductive surface can be an aircraft wing or a ship's hull (or even thepaint applied to the structure). U.S. Pat. No. 6,027,075 discloses afirst electrode connected with the surface; a nonconductive orelectrically insulating material is applied as a grid over the surface;and a second electrode is formed by applying a conductive material, forexample conductive paint, over the insulating material, but withoutcontacting the surface. A practical problem, however, with the gridelectrode system disclosed in U.S. Pat. No. 6,027,075 is formation ofthe grid electrodes and associated insulating layers. The individualcomponents of the grid system, including electrodes, wiring andinsulators, are fabricated on a small scale. Photolithographictechniques are capable of fabricating such grid systems.Photolithography is used very effectively in integrated circuitfabrication. The use of photolithography to form a grid system formodifying ice adhesion, however, is less suitable. It involves a largenumber of patterning and etching steps. Applied to ice controltechnology, photolithography is expensive, complicated and unreliable.

SOLUTION

The present invention replaces the grid described in U.S. Pat. No.6,027,075. An embodiment of the present invention provides a compositecoating comprising separate, closely spaced wire electrodes separated byinsulator fibers. The wire electrodes and insulator fibers are typicallywoven together using known and reliable industrial technologies. Thewire electrodes are connected alternately to a DC power source in such amanner to function as cathodes and anodes. The composite coating isdurable and flexible, and is typically applied to the surface to beprotected using conventional adhesives. The metal wires may be gold,platinum-plated titanium or niobium, or other material with highresistance to electro-corrosion. As dielectric insulator fibers, nylon,glass or other dielectric material may be used. The dielectric fiberskeep the metal electrodes apart, while providing coating integrity. Inaddition, the dielectric insulator fibers electrically insulate the wireelectrodes from the surface on which the composite coating is applied.Typical wire diameters are in the range of from 10 to 100 μm, with thesame range of open space between the electrode wires and insulatorfibers. If ice forms in and over the composite coating, a dc bias isapplied to the electrodes. As a result, the ice adhesion strength at theinterface of the ice and the surface of the object being protected ismodified.

In another embodiment of the invention, the wire electrodes of acomposite coating are connected to a DC bias source so that they havethe same DC bias. The surface on which the composite coating is appliedis electrically conductive and has an opposite DC bias. Ice formed inthe spaces of the composite coating close the electrical circuit.

In another embodiment of the invention, a wire mesh comprisingelectrically conductive wires is formed. The wire mesh is disposed on anelectrically conductive surface, with an insulating layer interposedbetween the wire mesh and the surface. A DC bias is applied to the wiremesh and an opposite DC bias is applied to the surface. Ice that isformed in the spaces of the wire mesh closes the electrical circuit.

Those skilled in the art should appreciate that the above-describedsystem can be applied to surfaces of many objects where it is desired toreduce ice adhesion strength, such as on car windshields, airplanewings, ship hulls and power lines. When the invention takes the form ofa composite cloth, it contains both the functional anodes and cathodesnecessary for the system to work. Therefore, it is not important whetherthe surface of the object to be protected is electrically conductive ornonconductive.

The invention is next described further in connection with preferredembodiments, and it will become apparent that various additions,subtractions, and modifications can be made by those skilled in the artwithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained byreference to the drawings, in which:

FIG. 1 shows a deicing system incorporating an electrical coating todeice surfaces in accord with the invention;

FIG. 2 shows an alternate deicing system incorporating an electricalcoating to deice surfaces in accord with the invention;

FIG. 3 depicts a composite coating having cathode wires and anode wiresin accordance with the invention that operates to modify the adhesion ofice formed on a surface;

FIG. 4 depicts a composite coating in accordance with the invention inwhich the electrode wires have the same bias; and

FIG. 5 depicts a wire mesh in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention includes methods, systems and structures which modify iceadhesion strength to objects such as metals and semiconductors byapplication of a DC bias to the interface between the ice and theobjects. FIG. 1 shows one system 10 incorporating an electrical deicingcoating 12 to affect ice 14 that might adhere to surface 16. Surface 16may for example be an airplane wing, helicopter blade, jet inlet, heatexchanger for kitchen and industrial equipment, refridgerator, roadsigns, ship overstructures, or other object subjected to cold, wet andice conditions. More specifically, coating 12 is applied over surface 16to protect surface 16 from ice 14. Coating 12 is preferably flexible soas to physically conform to the shape of surface 16. In operation, avoltage is applied to coating 12 by power supply 18. Typically thisvoltage is over two volts and generally between two and one hundredvolts, with higher voltages being applied for lower temperatures. By wayof example, for a temperature of −10C and an anode-to-cathode spacing of50 μm within coating 12 (described in more detail below), approximately20V is applied to coating 12 to provide 10 mA/cm̂2 current densitythrough very pure atomospheric ice such as found on airplane wings.

When voltage is applied, ice 14 decomposes into gaseous oxygen andhydrogen through electrolysis. Further, gases form within ice 14generating high-pressure bubbles that exfoliate ice 14 from coating 12(and hence from surface 16). Typical current density applied to coating12 is between about 1-10 mA/cm̂2. If desired, voltage regulator subsystem20 is connected in feedback with power supply 18, and hence with thecircuit formed by coating 12 and ice 14, so as to increase or decreaseDC voltage applied to coating 12 according to optimum conditions.

FIG. 2 shows one system 40 incorporating an electrical deicing coating42 to affect ice 44 that might adhere to conductive surface46.Conductive surface 46 may for example be an airplane wing, helicopterblade, jet inlet, heat exchanger for kitchen and industrial equipment,refridgerator, road signs ship overstructures, or other object subjectedto cold, wet and ice conditions. More specifically, coating 42 isapplied over surface 46 to protect surface 46 from ice 44. Coating 42 ispreferably flexible so as to physically conform to the shape of surface46. In operation, a voltage is applied between coating 42 and surface 46by power supply 48. The bias voltage applied to coating 42 may be equaland opposite to the bias voltage applied to surface 46. If desired, aninsulator 45 may be disposed between coating 42 and surface 46;insulator 45 preferably comprises a dielectric mesh configurationdescribed below.

Typically the voltage between coating 42 and surface 46 is over twovolts and generally between two and one hundred volts, with highervoltages being applied for lower temperatures.

When voltage is applied, ice 44 decomposes into gaseous oxygen andhydrogen through electrolysis. Further, gases form within ice 44generating high-pressure bubbles that exfoliate ice 44 from coating 42(and hence from surface 46). Typical current density applied to coating42 is between about 1-10 mA/cm̂2. If desired, voltage regulator subsystem50 is connected in feedback with power supply 48, and hence with thecircuit formed by coating 42, surface 46, and ice 44, so as to increaseor decrease DC voltage applied to coating 42 according to optimumconditions.

Systems 10, 40 thus modify the electrostatic interactions which form thebonding between ice and metals. These interactions are effectivelychanged (either reduced or enhanced) by application of the small DC(direct current) bias between ice and the metals. As described below,the composite coating comprises metal electrode wires separated bydielectric insulator fibers in a flexible format so as to be applied tosurface 16 needing protection from ice. By applying a dc bias, the iceadhesion strength between ice and the electrodes of coating, as well asbetween ice and surface, is modified.

Ice has certain physical properties which allow the present invention toselectively modify the adhesion of ice to conductive (andsemi-conductive) surfaces. If a charge is generated on the surfacecoming on contact with ice, it is possible to selectively modify theadhesion between the two surfaces. First, ice is a protonicsemiconductor, a small class of semiconductors whose charge carriers areprotons rather than electrons. This phenomenon results from hydrogenbonding within the ice. Similar to typical electron-basedsemiconductors, ice is electrically conductive, although this electricalconductivity is generally weak.

Another physical property of ice is that its surface is covered with aliquid-like layer (“LLL”). The LLL has important physicalcharacteristics. First, the LLL is only nanometers thick. Second, itranges in viscosity from almost water-like, at temperatures at or nearto freezing, to very viscous at lower temperatures. Further, the LLLexists at temperatures as low as −100° C.

The LLL is also a major factor of ice adhesion strength. The combinationof the semiconductive properties of ice and the LLL allows one toselectively manipulate ice adhesion strength between ice and otherobjects. Generally, water molecules within a piece of ice are randomlyoriented. On the surface, however, the molecules are substantiallyoriented in the same direction, either outward or inward. As a result,all their protons, and hence the positive charges, either face outwardor inward. While the exact mechanism is unknown, it is likely that therandomness of water molecules transitions to an ordered orientationwithin the LLL. However, the practical result of the ordering is that ahigh density of electrical charges, either positive or negative, occursat the surface. Accordingly, if a charge is generated on the surfacecoming on contact with ice, it is possible to selectively modify theadhesion between the two surfaces. As like charges repel and oppositesattract, an externally applied electrical bias at the interface of theice and the other surface either reduces or enhances the adhesion of theice to the other object.

Ice includes polar water molecules that strongly interact with any solidsubstrate which has dielectric permittivity different from that of ice.In addition, there is theoretical and experimental evidence for theexistence of a surface charge in ice. This surface charge can alsointeract with the substrate.

Electrolysis is an important factor. When a dc current flows throughice, gaseous hydrogen (H₂) and oxygen (O₂) accumulate at the iceinterfaces in the form of small bubbles, due to ice electrolysis. Thesebubbles play a role in the development of interfacial cracks, reducingthe ice adhesion strength.

FIG. 3 depicts a composite coating 100 having cathode wires 102 andanode wires 104, in accordance with the invention. Dielectric wires 106form an insulating weave about wires 102, 104 to prevent shorting. Wires102, 104 for example connect to power supply 18 (or supply 48) such thatappropriate current density affects ice adhering to coating 100.Typically, the current density is made to decrease adhesion strengthbetween ice and coating 100, such that coating 100 operates to protectsurfaces, such as surface 16, from ice. Typical spacings between wires102 are 10-50 μm; typical spacings between wires 104 are also 10-50 μm.Wires 102,104 are for example made from gold, platinum plated titaniumor niobium, or from metal with high resistance to electro-corrosion.

FIG. 4 depicts a composite coating 120 in accordance with the invention.Coating 120 has alternating electrode wires 122, each with equal biasfrom the connected power supply. Coating 120 may for example be appliedto surface 46 of FIG. 2, where surface 46 is conductive; a voltagepotential exists between surface 46 and wires 122. An insulating mesh124 prevents wires 122 from shorting, and further prevents shortingbetween wires 122 and surface 46. Ice 44 completes the circuit betweenwires 122 and surface 46 to invoke the ice adhesion modifications of theinvention.

FIG. 5 depicts a wire mesh coating 150 constructed in accordance withthe invention. Mesh coating 150 is generally conductive, with both wires152 and weave components 154 being conductive. Mesh coating 150 is thusapplied to conductive surface 46 with an insulator 45 disposedtherebetween. Insulator 45 is constructed so as to protect surface 46when ice 44 completes the circuit between mesh coating 150 and surface46. A voltage potential between mesh coating 150 and surface 46 modifiesthe adhesion strength of ice 44 as desired.

A typical current density applied to coatings of the invention are from1 to 10 mA/cm². Operating voltages are typically in the range of from 2to about 100 volts, depending on ice temperature and spacing betweenwires. The lower the temperature, the higher the voltage required. Thelarger the interwire spacing, the higher the voltage required. For atypical temperature of −10° C. and a spacing of 50 μm, a bias ofapproximately 20 volts provides a current density of about 10 mA/cm²through very pure ice.

It is important that anode wires 104, FIG. 3) have a very highresistance to anodic corrosion. For that, they may be coated with thinlayers of platinum or gold or amorphous carbon. Other alloys may also beapplied. Cathode wires 102 should also be impenetrable to hydrogen.Examples of good cathode material include gold, copper, brass, bronze,and silver.

A composite coating or wire mesh in accordance with the invention isflexible. It can protect a wide variety of surface materials and shapes,including, as examples: airplane wings, helicopter blades, protectivegrids on jet engine inlets, heat exchangers of kitchen and industrialrefrigerators, road signs, and ship superstructures.

The wire meshes and composite coatings described herein can befabricated using conventional methods used in industry. An inventivemesh or composite coating can be applied to a surface by simplystretching it over the surface with a thin layer of adhesive placedbetween the composite coating or mesh and the surface.

In view of the foregoing, what is claimed is:
 1. A system for modifyingice adhesion strength of ice adhered to an electrically conductivesurface, comprising: a composite coating having a wire mesh covering thesurface, the coating including electrically conductive wires; anelectrically nonconductive insulating layer between the coating and thesurface; and a DC power source for applying a DC bias between the meshand the surface via a circuit formed with the ice.
 2. A system as inclaim 1, further comprising an adhesive for adhering the compositecoating to the surface.
 3. A system as in claim 1, wherein the surfaceand the wire mesh are connected to opposing ends of the DC power source.4. A system of claim 1, wherein the DC bias provides between about 1-10mA/cm̂2 current density with the ice.
 5. A system of claim 1, wherein theDC bias provides between about 2-100 voltage potential between thesurface and the mesh.
 6. A system for modifying ice adhesion strength ofice adhered to an electrically conductive surface, comprising: acomposite coating covering the surface, the coating having a pluralityof electrically conductive electrode wires and a plurality ofelectrically insulating insulator fibers, the insulator fibersseparating each of the electrode wires from one other and insulating theelectrode wires from the surface; a DC power source for applying a DCbias between the electrode wires and the surface via a circuit formedwith the ice.
 7. A system as in claim 6, further comprising an adhesivefor adhering the composite coating to the surface.
 8. A system as inclaim 6 wherein the surface is connected to one end of the DC powersource and the electrode wires are connected the opposing end of said DCpower source.
 9. A system as in claim 6 wherein the electrode wiresinclude cathode wires and anode wires.
 10. A system as in claim 6wherein the composite coating is a composite cloth.
 11. A system as inclaim 10 wherein the composite cloth is woven from the electrode wiresand the insulator fibers.
 12. A system as in claim 11 wherein theelectrode wires are woven in a direction generally perpendicular to theinsulator fibers.
 13. A system of claim 6, wherein the electrode wiresare constructed from one of gold, copper, brass, bronze, silver andmixtures thereof.
 14. A system of claim 13, further comprising a coatingover the wires, the coating being selected from the group of platinum,gold and amorphous carbon.
 15. A system of claim 6, wherein theelectrode wires comprise anode and cathode wires, the power sourcealternately generating a bias between the surface and the anode wiresand between the surface and the cathode wires.
 16. A system formodifying ice adhesion strength of ice adhered to a surface, comprising:a composite coating covering the surface, the coating having a pluralityof cathode wires, a plurality of anode wires, and electricallyinsulating insulator fibers, the insulator fibers insulating the cathodewires from the anode wires; a DC power source for applying a DC biasbetween the cathode and anode wires via a circuit formed with the ice.17. A system as in claim 16 wherein the cathode wires are connected toone of the DC power source and the anode wires are connected to anotherend of the DC power source.
 18. A system according to claim 16, whereinthe DC power source is a battery.
 19. A system according to claim 16,wherein the surface comprises a surface of an aircraft wing.
 20. Asystem according to claim 16, wherein the surface comprises a surface ofa power line.
 21. A system as in claim 16, further comprising anadhesive for adhering the composite coating to the surface.
 22. A systemas in claim 16, wherein the composite coating is a composite cloth. 23.A system as in claim 22, wherein the composite cloth is woven from thecathode wires, the anode wires, and the insulator fibers.
 24. A systemas in claim 23, wherein the cathode and anode wires are woven in adirection generally perpendicular to the insulator fibers.
 25. A systemof claim 16, wherein the cathode wires are constructed from one of gold,copper, brass, bronze, silver and mixtures thereof.
 26. A system ofclaim 16, wherein the anode wires are constructed from one of gold,copper, brass, bronze, silver and mixtures thereof.
 27. A system ofclaim 26, further comprising a coating over the anode wires, the coatingbeing selected from the group of platinum, gold and amorphous carbon.